Our invention pertains to a probe for use in ultrasonically detecting flaws in objects such as castings and welds.
Ultrasonic flaw detection systems have found a widespread acceptance in various industries as a versatile, efficient tool for the detection of internal cracks, cavities, etc., in a variety of solid objects. They commonly include a probe to be held against the object. The probe comprises ultrasonic transducers for the transmission and reception of ultrasonic vibrations, arranged to determine the distance to a wave reflecting internal flaw in the object. High frequency electrical oscillations are transferred into mechanical vibrations which are sent out into the object. Any transmitted or reflected mechanical vibrations are received by the same probe, transferred back to electrical oscillations, and fed back through an amplifier for evaluation through display on a cathode ray tube. Japanese Laid Open Patent Applications Nos. 52-45388 and 52-87081 disclose examples of such ultrasonic probes.
Most of these and other known ultrasonic probes have had intrinsic "insensitive zones", where small flaws are not clearly detectable, immediately below the surface of the object being tested. We have found that such insensitive zones are attributable to the undue divergence of the ultrasonic beam generated by the prior art devices.
Another weakness of the known ultrasonic probes is that their performance is easy to be adversely affected by the irregular shape or roughness of the surface of the object under inspection. For this reason they have not necessarily been capable of detecting small flaws when held directly against weld beads or "black skins" of iron castings.
As an additional drawback, the known devices have mostly been capable of detecting flaws only in a limited region under the probe. Unnecessarily long time has had to be expended for inspecting greater regions.